Not Applicable
Not Applicable
This invention relates generally to coil or helical spring dampers used in valve assemblies of internal combustion engines and relates more particularly to such spring dampers which operate to inhibit oscillations of valve coil springs such that may occur in valve assemblies of internal combustion engines.
Internal combustion engines commonly used helical coil springs to bias combustion chamber valves to the closed position. At high engine speeds valve springs can resonate which can cause erratic valve operation. This can cause damage to the engine and in general impair engine performance. For example, impaired engine performance can occur when the vibration of a spring coil after the valve is closed causes the valve to slightly reopen. This is sometimes called valve bounce even though it may be caused by excessive spring vibration. Even a slight reopening of the valve after the valve is closed can result in a significant loss of power and efficiency.
This magnitude of the vibration of the valve spring coils is increased when the condition of resonance is reached which usually occurs at high engine speeds. Various techniques have been used to reduce valve spring vibration. One such technique is to increase the preload force and/or spring rate of the helical spring. This tends to reduce valve bounce and provide more stable operation. The disadvantage of this technique is that valve actuation forces are increased which results in increase frictional losses and increased fuel consumption. The increased spring forces will cause corresponding increases in spring stresses that can shorten spring life.
Another common technique used to damp spring vibration is the use of a device that uses friction to dissipate kinetic energy from vibrating spring coils. Such application or frictional dampers are shown in U.S. Pat. Nos. 4,538,563, 4,5009,473, 4,479,461, 3,336,913 and others. These types of dampers have the disadvantage of causing high temperatures due to the friction heating. Analysis has shown that the effectiveness of friction dampers is limited because of the magnitude of the frictional forces that will not cause excessive heating is too small to achieve significant damping.
It is the object of the present invention to provide a means for reducing the vibration of valve springs used in internal combustion engines with none of the disadvantages that exists when friction type dampers are used. The present invention also does not require increased spring forces to limited valve spring vibration and valve bounce. The present invention provides control to valve springs that will essentially prevent valve bounce from occurring.
Another object to the present invention to provide an assembly that is well suited for use in an internal combustion engines where little space may be available.
Computation simulations have shown that valve bounce due to spring vibrations can essentially be eliminated if the approximate-middle valve spring coil is restrained from extending a small distance past its static-equilibrium position. The static-equilibrium position of the middle coil is defined to be the position of the coil when the valve is close.
This invention resides in the area of the valve spring. Valve springs are usually helical and can involve concentric springs. With regard t this invention, a valve spring referrers to the spring assembly (including concentric springs) that act on an individual valve. The base of the valve spring, which does not move, rests on engine head. The opposite end of the valve spring is attached to the top of the engine valve commonly using a valve spring retainer. While the engine is running, this retainer end of the valve spring moves with a reciprocating motion that is driven by the camshaft. This invention involves the means for restraining the approximate-middle valve spring coil from extending past its approximate static-equilibrium position.
This invention involves the use of a strong member or members having the proper mechanical stiffness and which is attached to or extends around the mid-section of the coil. The other end of the member is attached to the base. When the valve is forced opened by the cam, this member permits the approximate-middle valve spring coil to move freely toward the base of the valve spring. When the valve is closed, the member restrains the approximate-middle valve spring coil from extending a small distance (on the order of 2 mm) past the position corresponding with the static-equilibrium position.
During the time that the valve is being closed, the approximate-middle valve spring coil can be moving with a high velocity and have significant kinetic energy. The previously mentioned member that is used to restrain this coil must be sufficiently strong and stiff to arrest the motion of the coil. If the member is too stiff, excessive impact forces can be developed and the member could fail because of the high forces caused by the shock loading. If the member is too compliant, the member will permit the approximately middle valve spring coil to move too great of distance past the static-equilibrium position and result in ineffective spring damping and control.
One method of restraining the approximate-middle valve spring coil is by the use of a strong and flexible cable. A plurality of cables could be attached to the coil or extend around the appropriate section of the spring coil. The opposite end of the cables could be attached to the fixed member such as the base of the spring or to the engine head. The cables would flex and permit the approximate-middle coil to move toward the spring base when the valve is opening. The cables are sufficiently strong and have the proper stiffness to stop the extension motion of the approximate-middle valve spring coil when this coil reaches it static equilibrium point. A plurality of cables acting in series along the circumference of the approximate-middle valve spring coil could be used to provide the necessary strength and stiffness.
In another embodiment of the invention, the fixed ends of the cables are connected to second members that have more compliance than the cables. These second members would in turn be connected to the fixed base. In this embodiment, the compliant second members would reduce the shock or impact loading that results when the approximate-middle valve coil spring is arrested.
In a further embodiment of the invention, a braided or twisted wire or cable could be used to provide additional compliance, which would reduce the shock or impact loading that results from stopping a moving coil.